What is useful about a reference-to-array parameter?

Question

I recently found some code like this:

typedef int TenInts[10];
void foo(TenInts &arr);

What can you do in the body of foo()

Answer 1

Shouldn't we also address the words in bold from the question:

What can you do in the body of foo() that is useful, that you could not do if the declaration was void foo(int arr[]);?

The answer is: nothing. Passing an argument by reference allows a function to change its value and pass back this change to the caller. However, it is not possible to change the value of the array as a whole, which would have been a reason to pass it by reference.

void foo(int (&arr)[3]) { // reference to an array
   arr = {1, 2 ,3};       // ILLEGAL: array type int[3] is not assignable
   arr = new(int[3]);     // same issue
   arr = arr2;            // same issue, with arr2 global variable of type int[3] 
}